With all the possible permutations between choices in ME3 and in previous ME games, how many different endings are there in the game and what is the most effective playthrough method to see all the endings?

@foxtrot I think the only difference between yours and mine is I'm simply looking for the major endings rather than all the little outcomes of every action you take in the entire series. Yours is more of a superset of mine, but I don't see why it was downvoted.
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z 'Mar 7 '12 at 16:57

Same here and thank you for clarification.
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Zero StackMar 7 '12 at 17:01

Readiness Rating 1750 – Choose to become a Reaper and the Earth will be destroyed.

Readiness Rating 1900 – Choose to destroy the Repears and the Earth will be somewhat -destroyed

Readiness Rating 2350 – Choose to become a Reaper and the Earth will be saved.

Readiness Rating 2650 – Choose to destroy the Reapers and Earth will be saved.

Readiness Rating 2800 – Earth and the Galaxy will be saved once you’re able to create synergy

Readiness Rating 4000 – Choose to destroy the Reapers and Save Anderson to see Shepard alive.

Readiness Rating 5000 – Choose to destroy the reapers and fail to save Anderson to see Shepard alive.

There are numerous ways to increase readiness and depending on your import save status, single player decisions, multiplayer skill, and multiplayer time, the "most efficient" way to manipulate readiness doesn't really have a universal answer for players.

is that right? a lower readiness rating (2350) for saving the collector base will result in earth only somewhat being destroyed but a higher one (2650 also saving the base) will result in the earth being completely destroyed?
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z 'Mar 7 '12 at 16:55

1

The source for this is the official Prima guide. It's not speculation.
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LessPop_MoreFizz♦Mar 8 '12 at 17:05

2

Worth noting that the Prima Guide contains errors elsewhere, such as saying Kaidan is only available as a romance option for female Shepards, and it does mention the "secret ending" no one has been able to verify, so we should perhaps take the guide's advice with a grain of salt. All that being said, the guide says that if you did not destroy the Collector's base, at 2350 Earth is "devastated but still there," not that it's destroyed.
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TeryxMar 13 '12 at 2:01